No, it is not true if you have a themostat, then there is no such thing as 'waste heat'. If you have a thermostat, there can still be such a thing as waste heat.
The positioning and timing of heaters around the house typically isn't random: heating devices are typically sited in particular places, facing particular directions, for a good reason: we want heat to be some place in particular.
A fridge and freezer will typically make one corner of your kitchen quite warm. Now, depending on air circulation and the surfaces behind it, much of that heat might be going out through an external wall. The same goes for the rest of waste heat: an incandescent lamp in the centre of a ceiling might only result in a warm centre of your ceiling that's no use at all.
Heating systems usually have time controllers on them, because it's rare to want heating on 24 hours a day, every day of the year. Waste heat from other appliances may be there when you don't want it, and may have leaked away by the time you did.
And anything that dumps heat year-round, in climates and buildings where part of the year is very hot, may be adding to the overheating.